1. Field of the Invention
This invention relates to a structure and a method for the detection of objects in particular the determination of plant status via remote sensing of plant biomass and plant biochemical properties for the purposes of mapping and applying agricultural products e.g. nitrogen based fertilizer.
2. Description of Related Art
In order to manage our natural resources in an efficient and cost-effective manner, producers and turf professionals need a way in which to measure and assess the health and performance of their landscapes. For example, the need to know when and how much fertilizer (nitrogen) and other nutrients to apply to a plant to elicit the appropriate growth response is primarily guess work to the producer. Because nitrogen is required by the plant in the greatest quantities and because nitrogen is rather mobile in soils, producers have practiced a one time application of nitrogen to cover the crops need for the entire growing season. However, over application of nitrogen on agricultural and commercial landscapes has resulted in the contamination of ground and surface waters. The primary vectors for water contamination are run-off and leaching. Nitrate-nitrogen is the most common contaminant found in U.S. groundwater. Nitrate contamination is increasing both in area and concentration, particularly beneath landscapes dominated by corn production. It is estimated that 1.8×109 kilograms of nitrates wash into the Gulf of Mexico from the Mississippi River basin each year. Of this amount, 55% of the nitrogen released into the basin can be attributed to agricultural fertilizers with only a 3% contribution attributable to non-agricultural fertilizer application primarily on turf for lawns and recreational land (CAST, 1999).
Techniques to remotely measure crop status include the use of a spectroradiometer and other instruments (Bausch et al. 1994; Chappelle et al. 1992; Maas and Dunlap, 1989), aerial photography (Benton et al, 1976), and satellite imagery.
The techniques listed above are not without their limitations. For example, early research by Resource21™ determined that during the optimal fly over times between 10 a.m. and 11 a.m. for satellite imaging, cloud cover had adverse affects on visibility. It was found that during the 10 am to 11 am time frame, fields in Colorado were visible approximately 80% of the time while eastern Nebraska fields were visible approximately 50% of the time. This trend in decreased visibility continued the farther east that data was collected. Also, spatial resolution for satellite imagery is poor (Landsat, 20 meter and panchromatic, 10 meter). Similar problems plague aerial photographic methods as well. While aerial imagery has better spatial resolution (typically less than 3 meters) than satellite imaging, partial cloud cover can shade sections of fields giving biased or incorrect reflectance measurements. Both techniques, however, suffer from the need for extensive data processing (performed by third party providers at high cost and long lead time) and geo-referencing issues. Even with spectroradiometric methods using sunlight as the ambient light source, cloud cover and time of day (8 a.m. to 8 p.m.) demands limit the mainstream acceptance of the technology for addressing the nitrogen rate over-loading problem. What is needed is an on-the-go type sensor that overcomes the time of day and fair-weather issues surrounding the aforementioned measurement techniques.
In certain crops or plant varieties, nutrient deficiencies constitute only part of the management problem. In particular, the basic problem of determining or monitoring plant status with respect to stress whether it stems from nutrient, water, pest, disease, or otherwise is of primary concern. For instance, turf stress determination is of major concern for the turf manager. Earlier detection can protect the health of the grass but also reduce the cost of restoring the badly damaged turf to good health. Turf stress can be due to many causes such as water, pest, nutrient, heat, disease, and the like. By detecting changes in the turf landscape early, turf quality can be maintained and costly restoration operations can be reduced or eliminated. On the other hand, being able to control the degree of stress is important for some producers. Grape producers, for example, like to control the degree of water stress prior to harvesting in order to control disease and increase the sugar content of the grape.